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Front. Microbiol. | doi: 10.3389/fmicb.2018.01430

Herbaspirillum seropedicae differentially expressed genes in response to iron availability

  • 1Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE), Uruguay
  • 2Departamento de Microbiología, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE), Uruguay
  • 3Departamento de Bioquimica e Biologia Molecular, Universidade Federal do Paraná, Brazil

Herbaspirillum seropedicae Z67 is a nitrogen-fixing endophyte that colonizes many important crops. Like in almost all organisms, vital cellular processes of this endophyte are iron dependent. In order to efficiently acquire iron to fulfill its requirements, this bacterium produces the siderophores serobactins. However, the presence in its genome of many others iron acquisition genes suggests that serobactins are not the only strategy used by H. seropedicae to circumvent the metal deficiency. The aim of this work was to identify genes and proteins differentially expressed by cells growing in low iron conditions in order to describe H. seropedicae response to iron limitation stress. For this purpose, and by using a transcriptomic approach, we searched and identified a set of genes up-regulated when iron was scarce . One of them, Hsero_2337, codes for a TonB-dependent transporter/transducer present in the serobactins biosynthesis genomic locus, with an unknown function. Another TonB-dependent receptor, the one encoded by Hsero_1277, and an inner membrane ferrous iron permease, coded by Hsero_2720, were also detected. By using a proteomic approach focused in membrane proteins, we identified the specific receptor for iron-serobactin internalization SbtR and two non-characterized TonB-dependent receptors (coded by genes Hsero_1277 and Hsero_3255). We constructed mutants on some of the identified genes and characterize them by in vitro growth, biofilm formation, and in interaction with rice plants. Characterization of mutants in gene Hsero_2337 showed that the TonB-dependent receptor coded by this gene has a regulatory role in the biosynthesis of serobactins, probably by interacting with the alternative sigma factor PfrI, coded by gene Hsero_2338. The mutant strains plant colonization is not affected, since the mutant strains colonize normally the root and aerial part of rice plants. These results suggest that strategies used by H. seropedicae to acquire iron inside plants are far more diverse than the ones characterized in this work. In vivo expression studies or colonization competition experiments between the different mutant strains could help us in future works to determine the relative importance of the different iron acquisition systems in the interaction of H. seropedicae with rice plants.

Keywords: iron-uptake, rice, H. seropedicae, TonB-dependent receptor, endophyte

Received: 28 Dec 2017; Accepted: 11 Jun 2018.

Edited by:

Essaid Ait Barka, Université de Reims Champagne Ardenne, France

Reviewed by:

Marc Ongena, University of Liège, Belgium
Sowmya Ramachandran, Washington State University, United States  

Copyright: © 2018 Trovero, Scavone, Platero, Souza, Fabiano and Rosconi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: PhD. Federico Rosconi, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE), Departamento de Bioquímica y Genómica Microbianas, Avenida Italia 3318, Montevideo, 11600, Montevideo, Uruguay, frosconi@iibce.edu.uy